Tuned exhaust gas system for outboard motor



G. E. MlLLER 3,520,270

TUNED EXHAUST GAS SYSTEM FOR OUTBOARD MOTOR Filed May 29, 1968 lUnitedStates Patent O 3,520,270 TUNED EXHAUST GAS SYSTEM FOR OUTBOARD MOTORGeorge E. Miller, Zion, Ill., assignor to Outboard Marine Corporation,Waukegan, Ill., a corporation of Delaware Filed May 29, 1968, Ser. No.733,159 Int. Cl. B63h 21/26 U.S. Cl. 115-17 13 Claims ABSTRACT F THEDISCLOSURE,

The invention provides an exhaust gas passage extending in an outboardmotor lower unit from an engine exhaust gas port to an exhaust gasdischarge outlet located below the water level around the lower unit,and including an exhaust gas tube which extends through the lower unitdriveshaft housing in spaced relation to the walls of said housing toprevent contact of exhaust gases with such outer walls and which isprovided with an upper part and a lower part of greater transverse crosssection than the transverse cross section of the upper part. Enlargementof the lower part of the exhaust gas tube in relation to the upper partserves to produce, in response to exhaust gas flow, negatively reflectedpressure waves which arrive at the engine cylinder at about the timewhen the piston is at bottom dead center and thereby provide improvedscavenging of the burnt combustion gases.

BACKGROUND OF INVENTION This invention relates generally to outboardmotors. More particularly, the invention relates to exhaust gasdischarge systems for outboard motors and specifically to exhaust gassystems including an exhaust gas tube which extends within thedriveshaft housing in isolated and spaced relation to the outer housingwalls and upwardly from below or approximately the normal level of thewater surrounding the housing. Examples of such tubes are found in theLarsen Pat. 3,198,162, the Kollmann Pat. 3,310,022 and the Boda Pat.3,350,879.

Such systems have not always achieved optimum horsepower output due tothe construction of the exhaust gasl pasageway. In at least oneinstance, it is believed that the silencing features of the inventiondisclosed in the Larsen Pat. 3,198,162 were not employed because ofadverse affect on horsepower output. The invention herein disclosedfacilitates use of the silencing system disclosed in the Larsen Pat.3,198,162 while at the same time maximizing horsepower output.

SUMMARY OF INVENTION The invention relates to maximizing the horse poweroutput of an outboard motor having an exhaust gas passage comprising anexhaust gas tube located in a drive shaft housing in spaced relation tothe outer walls of the drive shaft housing such that the exhaust gasesare normally prevented from contacting such outer walls. Suchmaximization is provided by employing negatively reflected pressurewaves, i.e., the negative reflection of the compressive wave produced bythe discharging exhaust gases, to assist in scavenging the burnedcombustion ICC products. Specifically, the invention involves producingsuch negative pressure waves, i.e., pressure waves below the meanexhaust manifold pressure, by enlarging the lower portion of the exhaustgas tube and locating the commencement of enlargement at a distance fromthe engine cylinder or cylinders such that negative pressure wavesarrive back at the cylinders approximately when the pistons are atbottom dead center.

The disclosed invention therefore provides an outboard motor having anexhaust gas tube which is situated in spaced relation from the driveshaft housing walls, which is arranged to prevent exhaust gas contactwith the outer walls of the drive shaft housing, and which has upper andlower portions, with the lower portion having an enlarged crosssectional area as compared to the upper portion and with the upper andlower parts being connected at a juncture located above the cavitationplate or water line under normal operating conditions.

In addition to the foregoing, the invention involves the extension ofthe upper portion of the tube slightly into the lower portion to providea depending lip or flange which projects into the lower portion andserves to increase the scavenging efficiency of the returning waves.

The invention is preferably embodied in an exhaust gas system in whichthe exhaust gas tube is resiliently mounted and water jacketed todiminish transmission of exhaust gas excitations to the outer walls ofthe drive shaft housing.

Other objects and advantages of the invention will become known byreference to the following drawings and accompanying description inwhich:

In the drawings:

FIG. 1 is a side-elevational view, partially broken away and in section,and partially schematically of an outboard motor embodying various ofthe features of the invention;

FIG. 2 is a view taken along line 2-2 of FIG. 1;

FIG.y 3 is 'a cross sectional elevational view of a modified exhaust gastube for use in the motor shown in FIG. 1; and

FIG. 4 is a cross sectional elevational view of another modified exhaustgas tube for use in the motor shown in FIG. l.

GENERAL DESCRIPTION Shown in the drawings is an outboard Imotor 11comprising a transom clamp or bracket 13 which is pivotally connected bya horizontal pivot 15 to a swivel bracket 17. In turn, the swivelbracket 17 is pivotally connected about a vertical pivot 19 to apropulsion unit 21 including a power head 23 and a lower unit 25 whichsupports the power head 23 and includes an intermediate housing or strut27 connected to the power head 23, together with a gear box 29 which islocated at the bottom of the housing 27, which is suitably connected tothe housing 27 by a series of bolts 30, and which, in normal operation,is submerged in water. Above the gear box in the conventional locationis a cavitation plate 32 which, under normal operating conditions, islocated at or slightly below the water level aft of the boat transom.The power head 23 includes an engine 31 having one or more cylinders 33with pistons 35 reciprocable therein, an output or crankshaft 37, and anexhaust gas discharge port 39.

Also included in the outboard motor 11 is an engine cooling systemincluding an engine cooling jacket 45 having an inlet 47 and a dischargeoutlet or port 49. Water for the cooling jacket is supplied to the inlet47 through a conduit 51 from a water pump 53 which is communicable witha lake or stream and which is driven by a drive shaft 55 extendingthrough the housing 27 and connected to the crankshaft 37. Thedriveshaft 55 extends into the gear box 29 and connects with atransmission or `clutch 57 controlling delivery of power to a propellershaft 59 carrying -a propeller 61 rearwardly of the gear box 29.

The engine cooling system can take various forms and can be either ofthe recirculating type or of the non-reciroulating type. The clutch ortransmission can also take various forms and can be either mechanical,electro-mechanical, hydraulic or electro-hydraulic.

Included in the lower unit 25 is an exhaust gas system for conductingexhaust -gases from the engine exhaust gas discharge port to anunderwater discharge outlet which is located below the surrounding waterlevel during normal operation and more or less near the bottom of thelower unit. In the disclosed construction, the exhaust gas systemincludes an exhaust gas passage 65 having an underwater exhaust gasdischarge outlet 67 provided by a passage section 69 formed in thehollow interior of the hub of the propeller 61. In turn, the propellerhub passage section 69 communicates with a gearbox passage section 71which, in turn, communicates with an exhaust Igas tube or pipe 73extending upwardly from approximately at or below the water level 75during normal operations. The exhaust gas tube or pipe 73 communicateswith the engine exhaust gas port 39 and is arranged to prevent contactof the exhaust gases with the 'walls of the drive shaft housing. Ifdesired, the exhaust gas discharge outlet could be provided in a iinportion of the lower unit as shown in the Larsen Pat. 3,198,162.

As also disclosed in the Larsen Pat. 3,198,162, the tube 73, at least atthe bottom, is preferably vibrationally isolated from the drive shafthousing by means of one or more resilient elastomeric mounts or supports77, such as for instance a rubber ring or blocks of rubber or the like,to prevent vibration transmission from the tube 73 to the drive shafthousing 27.

As also disclosed in the Larsen Pat. 3,198,162, the tube 73 ispreferably surrounded with a jacket 79 of water to assist in deadeningtransmission of exhaust gas excitations to the outer walls of the driveshaft housing 27 In this regard, in the disclosed construction, thedrive shaft housing 27 includes a generally vertically extending crosspartition 83 which forms, together with other portions of the driveshaft housing 27, a chamber for the water jacket. Water can be suppliedto the jacket or chamber in various ways. In the disclosed construction,such water is supplied from the engine water jacket discharge port 49.Excess water from the exhaust gas tube water jacket 83 overflows over aledge 87 and to the exterior of the drive shaft housing 27 through aport 89 in the rear outer wall 91 of the drive shaft housing. Ifdesired, the overow discharge water can be conducted within the lowerunit 25 to a discharge point below the normal level of the surroundingwater.

In accordance with the invention, the exhaust gas tube is constructed tomaximize power output from the engine by causing the production ofnegatively reflected pressure waves which travel back to the enginecylinders 33 and can be -employed to assist in scavenging the enginecylinder or cylinders. Thus, in the disclosed construction, the exhaustgas' tube 73 includes a lower part or portion 94 which is materiallylarger in horizontal cross section than an upper part or portion 97 ofthe tube 73. As shown in FIG. 1 of the drawings, the lower tube part 94is joined to the upper `tube part 97 adjacent the lower end of the uppertube part along a junction located above the cavitation plate 32 orwater line 75 under normal operating 75 conditions. Very high efciencyin producing negative or reflected pressure waves can Ibe obtained bydesigning such that `the ratio of the lower portion horizontal crosssection to the upper portion horizontal cross section is 5 to 1. Becauseof size and mass flow limitations, as well as other considerations inthe construction of outboard motors, achievement of such a relativelylarge ratio has thus far not seemed practical. However, the advantagesof the invention can be obtained with a material increase in horizontalcross sectional size or area between the upper and lower portions of theexhaust gas tube. One engine which has been constructed and which has aratio of 2.3 to 1 provides substantial advantages. However, thisinvention is not limited to a ratio of 5 to 1 or 2.3 to 1 and it isexpressly stated that ratios smaller than 2.3 to 1 can be used toachieve the advantages of the invention.

Use of the returning negative pressure waves to assist in scavenging thecylinders is afforded by locating the enlargement in the exhaust gastube 73 at such distance from the cylinders that the returning pressurewaves will arrive at about the time the piston is at bottom dead center.The distance chosen can be such as to have maximum effect when at high,low, or middle engine speeds.

The enlarged portion 95 of the exhaust gas tube 73 can take variousforms. For example, in FIG. 1 the enlarged lower portion has a fore andaft length A approximately twice the transverse width B which, in turn,is somewhat larger than the diameter D of the circular cross section ofthe upper portion 97 of the exhaust gas tube 0r pipe 73.

The cross section of the lower portion of the exhaust gas tube shown inFIG. 1 is essentially generally constant throughout its vertical length.However, at least some of the advantages of the invention can beobtained when using an enlarged portion which, as shown in FIG. 4,diverges downwardly, i.e., gradually increases in horizontal crosssection in a downward direction from a junction between the lowerportion 195 and the lower end of the upper portion 197, which junctionis located above the cavitation plate 32 or normal water line undernormal operating conditions. Thus, the tube 173 shown in FIG. 4 divergesat its lower end to provide a horizontal cross section of graduallyincreasing size in the downward direction.

Another embodiment of an exhaust gas tube 273 in accordance with theinvention is shown in FIG. 3, which tube includes an upper part 297, anda lower part or enlarged portion 295, and a junction between the lowerpart 295 and the upper part 297 adjacent the lower end thereof, whichjunction is located above the cavitation plate 32 or normal water line7'5 under normal operating conditions. The lower enlarged portion 295includes two subparts, the upper sub-part 201 having a horizontal crosssection larger than that of the upper portion 297 of the exhaust gastube 273 and the lower sub-part 203 having a horizontal cross sectionalarea greater than the horizontal cross sectional area of the uppersub-part 201.

As already indicated, the increase in cross sectional area of the lowerportion as compared to the upper portion of the exhaust gas tube neednot be symmetrical about a vertical axis.

As also shown in FIG. 1, it is preferred to construct the exhaust gastube 73` so that the upper portion 97 extends slightly into the lowerportion 95, rather than terminating the upper portion 97 at the top ofthe lower or enlarged portion 95. Thus, in FIG. 1, there is provided alip or ange 98 which constitutes an extension of the upper portion 97 ofthe pipe 73 and which extends slightly 'into the lower portion 95 beyondthe upper wall 99 of the lower portion. A similar lip or flange 298 isshown in FIG. 3 extending from the upper portion 297 into the uppersub-part 201 of the lower or enlarged portion 296. Likewise, a lip orflange 398 extends a slight distance from the upper sub-part 201 intothe lower sub-part 203 of the enlarged portion 295. If' desired, such alip or flange can also Ibe employed in the tube 173 between the upperportion 197 and the lower portion 195.

The use of lips 98, 2.98y and 398 serves to increase the magnitude ofthe returning wave as compared to a returning wave which is producedwithout such a lip.

In operation, exhaust gases discharged froml the engine .31 travelthrough the exhaust pipe 73, and incident to passage from the upper part97 to the lower part 95 of thepipe 73,'produce negatively reectedpressure waves which travel .rearwardly and -upwardly through theexhaust gas tub'e 73 toward the cylinder,`arriving at the cylinder atapproximately the time when the piston is at bottom dead center. Thenegative pressure which therefore occurs adjacent to the cylinder servesto assist in removing from the cylinder all of the burnt combustiongases, thereby improving scavenging eiciency.

In operation, various of the features of the invention are set forth inthe following claims.

I claim:

1. In an outboard motor, the combination of a propulsion unit includinga power head having an exhaust gas port and a lower unit including ahousing supporting said power head, an exhaust gas discharge outletlocated below the water level around said lower unit under normaloperating conditions, and an exhaust gas passage extending from saidexhaust gas port to said exhaust gas discharge outlet and including anexhaust tube extending through said housing interiorly of the walls ofsaid hous ing, said exhaust gas tube including an upper part, a lowerpart of greater transverse cross section than the transverse crosssection of said upper part, and a junction between said lower part andsaid upper part adjacent the lower end of said upper part, said junctionbeing located above the water line under normal operating conditions.

2. An outboard motor in accordance with claim 1 wherein said upper partextends slightly into said lower part to provide a lip projectingslightly into said lower part.

3. An outboard motor in accordance with claim 1 wherein said tubeextends upwardly from adjacent to or below said water level.

4. An outboard motor in accordance with claim 1 wherein said lower partincludes a series of sub-parts, the lower sub-part of each adjacent pairof sub-parts having a horizontal transverse cross section larger thanthe horizontal transverse cross section of the upwardly adjacentsub-part.

5. An outboard motor in accordance with claim 1 wherein said lower partdiverges downwardly.

6. An outboard motor in accordance with claim 1 wherein said power headincludes a plurality of cylinders and pistons reciprocable in saidcylinders, and wherein said lower part is spaced from said cylinderssuch that negative pressure waves reliected incident to exhaust gaspassage from said upper part to said lower part return to said cylindersapproximately when said pistons are at bottom dead center.

7. In an outboard motor, the combination of a propulsion unit includinga power head having an exhaust gas port and a lower unit including ahousing supporting said power head, an exhaust gas discharge outletlocated below the water level around said lower unit under normaloperating conditions, an exhaust gas discharge passage extending fromsaid exhaust gas port to said exhaust gas discharge outlet and includingan exhaust tube extending through said housing in spaced relation to thewalls of said housing, said exhaust gas tube including an upper lpart, alower part of greater transverse cross section than the transverse crosssection of said upper part, and a junction between said lower part andsaid upper part adjacent the lower end of said upper part, said junctionbeing located above the water line under normal operating conditions, awater pump, and means for supplying water from said pump to the spacebetween said tube and the walls of said housing to provide a waterjacket around said tube.

8. An outboard motor in accordance with claim 7 including a resilientmount supporting said tube from said lowere unit.

9. An outboard motor in accordance with claim 7 wherein said upper partextends slightly into said lower part to provide a lip projectingslightly into said lower part.

10. An outboard motor in accordance with claim 7 wherein said power headincludes a plurality of cylinders and pistons reciprocable in saidcylinders and wherein said lower part is spaced from said cylinders suchthat negative pressure waves reflected incident to exhaust gas passagefrom said upper part to said lower part return to said cylindersapproximately when said pistons are at bottom dead center.

11. In an outboard motor, the combination of a transom bracket, a swivelbracket connected to said transom bracket about a horizontal pivot, anda propulsion unit connected to said swivel bracket about a verticalpivot, said propulsion unit including a power head having an internalcombustion engine with a plurality of cylinders, a plurality of pistonsreciprocable in said cylinders, an exhaust gas port and a water jackethaving a discharge port, and a lower unit including a housing supportingsaid power head, a gear box connected to the bottom of said housing andextending into the water under normal operating conditions, an exhaustgas discharge outlet located below the water level around said lowerunit under normal operating conditions, an exhaust gas passage extendingfrom said exhaust gas port to said exhaust gas discharge outlet andincluding an exhaust tube extending through said housing in spacedrelation to the walls of said housing and upwardly from adjacent to orbelow said water level, said exhaust gas tube including a lower part, anupper part, and a junction between said lower part and said upper partadjacent the lower end of said upper part, said junction being locatedabove the water line under normal operating conditions, said upper parthaving a horizontal transverse cross section less than the horizontaltransverse cross section of said lower part, said upper part extendingslightly into said lower part to provide a lip projecting slightly intosaid lower part, said lip being spaced from said cylinders such thatpressure waves reflected incident to exhaust gas passage from said upperpart to said lower part return to said cylinders approximately when saidpistons are at bottom dead center, a resilient mount supporting saidtube from said lower unit, a water pump communicating with said enginewater jacket, and means for supplying water from said engine waterjacket discharge port to the space between said tube and the walls ofsaid housing to provide a water jacket around said tube.

12. In an outboard motor, the combination of a propulsion unit includinga power head having an exhaust gas port and a lower unit including ahousing supporting said power head, a cavitation plate, an exhaust gasdischarge outlet located below the water level around said lower unitunder normal operating conditions, and an exhaust gas passage extendingfrom said exhaust gas port to said exhaust gas discharge outlet andincluding an exhaust tube extending through said housing interiorly ofthe walls of said housing, said exhaust gas tube includingg and upperpart, a lower part of greater transverse cross section than thetransverse cross section of said upper part, and a junction between saidlower part and said upper part adjacent the lower end of said upperpart, said junction being located above said cavitation plate.

13. In an outboard motor, the combination of a propulsion unit includinga power head having an exhaust gas port and a lower unit including ahousing supporting said power head, a cavitation plate, an exhaust gasdischarge outlet located below the water level around said lower unitunder normal operating conditions, an exhaust gas discharge passageextending from said exhaust gas port to said exhaust gas dischargeoutlet and including an exhaust tube extending through said housing inspaced relation to the Walls of said housing, said exhaust gas tubeincluding an upper part, a lower part of greater transverse crosssection than the transverse cross section of said upper part, and ajunction between said lower part and said upper part adjacent the lowerend of said upper part, said junction being located above saidcavitation plate, a water pump, and 1 neans for supplying water fromsaid pump to the space between said tube and the walls of said housingto provide a water jacket around said tube.

References Cited UNITED STATES PATENTS Hansson 181-72 Ringles 181-57Nowak 181-72 Larsen 115,-17 Kollman 115-,-17

Walther et i. 181-57 X 10 ANDREW H. FARRELL, Primary Examiner

